Coated cemented carbide products

ABSTRACT

A coated cemented carbide product comprising a cemented carbide substrate and a fully dense hafnium and/or zirconium carbonitride coating on the substrate. The hafnium or hafnium and zirconium carbonitride coating has a carbon-to-nitrogen ratio having an Xray diffraction lattice parameter between 4.570 and 4.630 angstrom units while the zirconium carbonitride range is between about 4.600 and 4.620 angstrom units. The coated products are prepared by passing a hafnium or zirconium halide, hydrogen gas, nitrogen gas and a hydrocarbon gas over the carbide substrate at a temperature of from 1,000*-1,300* C., the relative proportion of nitrogen and hydrocarbon and the temperature being adjusted to obtain the foregoing carbon-to-nitrogen ratios in the coating.

KR 5925549991. 5R- 1 COATED CEMENTED CARBIDE PRODUCTS Thomas E. Hale, Warren, Mich.

Inventor:

Assignee: General Electric Company,

Schenectady, N.Y.

Filed: Feb. 11, 1972 Appl. No.2 225,667

References Cited I UNITED STATES PATENTS 2/1961 Urahiotes et a1. 117/106 12/1967 Rich et al. l17/l06 4/1972 Reedy 148/166 2/1973 Kieffer at al. 117/106 c 7/1973 Kalish 117/169 I Dec. 17, 1974 Primary Examiner-Douglas J. Drummond Assistant Examiner-.1. W. Massie [57] ABSTRACT A coated cemented carbide product comprising a cemented carbide substrate and a fully dense hafnium and/or zirconium carbonitride coating on the substrate. The hafnium or hafnium and zirconium carbonitride coating has a carbon-to-nitrogen ratio having an X-ray diffraction lattice parameter between 4.570 and 4.630 angstrom units while the zirconium carbonitride range is between about 4.600 and 4.620 angstrom units. The coated products are prepared by passing a hafnium or zirconium halide, hydrogen gas, nitrogen gas and a hydrocarbon gas over thecarbide substrate at a temperature of from l,000-l ,300" C., the relative proportion of nitrogen and hydrocarbon and the temperature being adjusted to obtain the foregoing carbon-tonitrogen ratios in the coating.

6 Claims, No Drawings 1 COATED CEMENTED CARBIDE PRODUCTS This invention relates to,a coated cemented carbide product and to a process for its preparation.

are preferred because they are less reactive with steel 7 workpieces at high machining speeds. The use of carbides other than WC generally results in a significant strength reduction, however, which limits either the amount of TiC and other carbides that can be added or the severity of the application when large amounts of TiC are used.

It is known that the wear resistance of cemented carbides can be enhanced by the application of a thin coating of certain hard substances such as TiC and TiN. In this manner a better combination of toughness and metal-cutting wear resistance is obtained than can nor- .mally be obtained using uncoated compositions. However. the toughness of TiC- and TiN-coated compositions is significantly less than that of the core or substrate material alone, apparently due to the low resisv b having a significantly higher strength as measured by the transverse rupture test.

The process of the invention involves the passage of a gaseous mixture of a hafnium or zirconium halide, hy-

drogen, nitrogen, and a hydrocarbon over the carbide substrate at temperatures between l,000-l,300 C. The relative proportions of carbon and nitrogen in the coating are varied by changing the relative amounts of nitrogen and hydrocarbon in the coating gas and by varying the deposition temperature.

The term cemented carbide" as used herein means one or more transitional carbides of a metal of Groups IVb, Vb, and VIb of the Periodic Table, cemented or bonded by one or more matrix metals selected from the Group Fe, Ni and Co. A typical cemented carbide'may contain WC in a'cobalt matrix or TiC ina nickel 'matrix. By fully dense coating is meant a coating of at least 99 percent of theoretical density and in most cases greater than 99.5 percent.

The starting materials are preferably hafnium or zirconium tetrachloride vapor, hydrogen gas, nitrogen gas, and methane gas. Other hafnium or zirconium halides and other hydrocarbons may be used, although 7 the foregoingstarting materials are preferred because tance of TiC and TiN to cracking and the high sensitivity of the substrate carbide to the presence of surface cracks. While it is likely that any coating that is hard and brittle will lower the strength of the coated cemented carbide composite if adherently bonded to the substrate. it is desirable to minimize the strength loss to as great an extent as possible. A 5 to 7 micron thick coating of TiC or TiN on metal-cutting grades of cev series ol coated products were prepared in accormented carbide causes a strength loss of 40-50 percent as measured by the bend or transverse rupture strength test. The reduced toughness of these coated composites is observed in actual use as an increased tendency breakage in some of the more severe applications.

it is accordingly an object of this invention to provide a coated cemented carbide composite that has a combination of strength and wear resistance that is superior to those presently known.

It is an additional object of this invention to provide a process for producing a firmly adherent, nonporous, dense coating on a cemented carbide substrate.

The foregoing and other objects of this invention are achieved by the chemical vapor deposition of a hafnium or zirconium carbonitride coating on a cemented carbide substrate. The product contains a cemented carbide substrate and a nonporous, dense hafnium and- /or zirconium carbonitride coating firmly and metallurgically bonded to the substrate. The desired coating will normally be from [-7 microns thickness. It has been found that it is necessary to carefully control the carbon-to-nitrogen ratio of these coatings since the metal-cutting performance is strongly dependent upon the value of this ratio, as will be explained in more detail subsequently. The coated products exhibit metalcutting performance that is substantially equal to or superior to currently available coated composites while they are the least expensive and most readily available raw materials. it is possible that small amounts of other halides, as'for example titanium, tantalumor nobium chloride, maybe included with'the zirconium or hafnium halide without detrimental effects on the properties of the it oated roduct and it is not intended to exclude the res of one or mor such ad "difiona metal carbides in the final product. in place of methane, propane or carbon tetrachloride may be used or any other hydrocarbon conventionally used as a sourceof carbon in vapor deposition processes.

dance with the process of the invention by passing hafnium or zirconium tetrachloride vapor, hydrogen, ni-

' trogen, and methane over cemented carbide inserts.

, and 11 below illustrate the manner in which variations in the relative proportions of carbon and nitrogen in the coating were obtained. if different coating temperatures, pressures, and hafnium or zirconium halides are used it is expected that different relative proportions of nitrogen and hydrocarbon will be required to obtain a desired carbon-to-nitrogen ratio in the coating. The carbon-to-nitrogen ratios shown in Tables I and II are estimated from X-ray diffraction lattice parameter measurements, assuming a linear relationship between lattice parameter and carbon-to-nitrogen ratio. Since the actual relationship is probably not exactly linear, the coating compositions of this invention are best characterized by their measured X-ray lattice parameters.

TABLE 1 COATING CONDITIONS EMPLOYED TO OBTAIN HfC.N COATINGS Gas Composition Coatin Ia m ce C/N Temp. Time Thickness Parameter Ratio Examples C. (Hm) Z H Z N, 5% CH HFCI, Microns A (Est) l 1000 1% 24 75 I l 1' 4.559 .50 2 1100 2 75 24 1 I 3 4.571 .75 3 1130 5 24 75 I 1 4 4.589 1.38 4 1 I50 1% 24 75 l l 2 4.607 2.70 5 1 170 5 24 75 1 1 5 4.621 5.25 6 1050 I 98 2 1 2 4.640

' ure TABLE II COATING CONDITIONS EMPLOYED TO OBTAIN 71C ,N COATINGS G25 Comgggition Coating r C/N Temp. Time Thickness Parameter 'Ratio' Examples C.' (Hrs) H %N, ZCI-L 952x0 Microns A (st.)

7 1150 2 24.00 75 0. 1 3-5 4.574 .031 8 1100 4% 23.75 75 0.25 I 4 4.583 .11 9 1135 4 23.67 75 0.33 I 5 4.602 .35 10 1135 2 23.60 75 0.40 I 8 4.611 .48 I1 [I50 2 23.50 75 0.50 I 4 4.617 .61 12 1100 3 87.50 10 L50 I 1.5 4.625 .79

to nitrogen ratio in the coating. The cutting time to a flank wear or crater depth of .010 inch is shown as a measure of cutting performance. Examples 18 and 19 had thicker coatings, in the 4 to 5 micron range. For comparison purposes the cutting performance of the uncoated substrate material, Example 20, and a 5 mi- 9 cron thick TiC coated insert, example 21, are also shown in Table III.

TABLE III CUTITNG PERFORMANCE OF HAFNIUM CARBONITRIDE COATED TOOLS (CUTTING SAE 1045 STEEL. 190 BHN. AT 700 SFPM SPEED) Coatin Character Cuttin Performance I; ttlcc UN Itme to Thickness Parameter Ratio .010" Wcar Example Microns A (Est. Min.

13 1.5 2 4.574 .82 I6 14 1.5 2 4.582 1.08 22 15 1.5 2 4.607 2.71 34 I6 2' 4.620 4.90 I7 1.5-2 4.64 ==(pure HfC) 10 18 4 5 4.587 1.32 I9 4 5 4.597 1.82 20 0 (uncoated substrate) 5 2| 5 (TiC coated) 22 The preferred temperature range for deposition of 50 It can be seen that the cutting performance of the cethe coating is l.000-1.300 C. At lower temperatures the deposition rate becomes very low and at higher temperatures excessive interaction occurs between the coating and the cemented carbide substrate.

The metal-cutting performance of cemented carbide inserts coated with hafnium carbonitride in accordance with this invention is shown in the following Table III. In Table III. examples 13 through 19 were k inch X V2 inch X 3/16 inch disposable cutting inserts, coated with hafnium carbonitridc at l.000l.l70 C. by the vapor deposition technique disclosed above for examples I through 6. The cemented carbide substrate was 72% WC, 8% TiC. 11.5% TaC, and 8.5% Co. Two levels of coating thickness, 1.5 2 microns and 4-5 microns. were prepared. These inserts were then used to machine SAE 1045 steel. 190 Bl-IN hardness, at 700 surfacefeet-per-minute speed. .010 inches-per-revolution feed, and .100 inches depth of cut. Examples 13 through 17 all had coating thicknesses in the 1.5 2 micron range and are listed in order of increasing carbon mented carbide tool material is very substantially improved by the hafnium carbonitride coating. It is also evident that the amount of improvement obtained is strongly dependent upon the carbon to nitrogen ratio with a peak in performance at about 4.61 angstrom units. It is probable that thicker coatings of 5 to 10 microns will provide an additional increment of improvement. When compared with the performance of the 5 micron thick TiC coated insert, it is evident that a substantial performance advantage is obtained for the 1.5 2 micron hafnium carbonitride coated inserts at or near the optimum composition and that a very substantial advantage is obtained when the hafnium carboni tride coating thickness is equal to that of the TiC coatmg.

The strength of the hafnium carbonitride coated composites was measured using a transverse rupture test that comprised three roll loading with a test span to thickness ratio of 3.5 to 1. Using this test it was found that the strength of hafnium carbonitride coated when the carbon to nitrogen ratio is at the optimum value of about 3 (lattice parameter of about 4.610 A). useful performance is obtained within a composition range of 4.57 to 4.63 A, which represents a carbon to nitrogen ratio range of about .73 to 12. The metal-cutting performance of zirconium carbonitride coated inserts prepared in accordance with this invention is shown in the following Table W. In

Table lV, Examples 22 through 32 were a inch X A inch X 3/ l6.inch disposable cutting inserts, coated with zirconium carbonitride at l;-100'-l, 15'0 C. by the vapor deposition technique disclosed above for Examples 6 through'l2. The cemented carbide substrate was tride, upon the carbon-'to-nitrogen ratio with a strong parameter of about I 4.610 was about 190,000 psi. The strength of 5 microns thick TiC-coated composites (using the same substrate carbide) was 150,000. It is therefore evident that zirconium carbonitride-coated composites having the optimum carbon-to-nitrogen ratio for metal cutting possess a superior combination of metal-cutting performance and strength when compared with TiC-coated composites.

in addition to the pure hafnium carbonitride and zirconiumcarbonitride coatings described above. a few coatedinser-ts were preparedin which the coating was 72% WC, 8% TiC, ll.5% TaC, and 8.5% Co. A range of coating thicknesses from 2.5 to 8 microns was obtained. These inserts were-then used to machine SAE i045 steel, 190 BHN hardness, at 700 surface-feet-per-.

minute speed. .010 inches per revolution feed, and .100

.25 inches depth of cut. The Examples 22-32 are listed by order of increasing carbon-to-nitrogen ratio in the coating, and cutting time to a flank wear of .010 inch is shown as a measure of cutting performance, For comparison purposes. the cutting performance of the coated insert. Example 34. is also shown in Table IV.

TABLE IV METAL CUTTING PERFORMANCE OF ZlRCONlUM CARBONlTRlDE TOOLS (CUTTING SAE 1045 STEEL. I90 BHN. AT 700 SFPM SPEED) Cutting Coatin Character Etttce Time to Thickness Parameter 0l0" Wcar Example Microns A Est. C/N (Min.)

22 2.5 4.583 .1 l 6.5 23 3. 4.595 .25 ll. 24 3. 4.60] .33 ll. 25 5. 4.602 .35 ll).

26 3. 4.606 .41 l4. 27 5. 4.609 .45 26. 28 8. 4.6ll .48 23. 29 3.5 4.612 .50 20. 30 5. 4.613 .53 i7. 3| 4. 4.6[6 .58 16. r 32 3. 4.620 .67 i3. 33 uncoated 5.

- substrate 34 $.(TiC 22.

coated) It can be seen that the cutting performance of the cemented carbide tool material is very substantiallyimcomposed of a solid solution of both hafnium and zirconium carbonitride. This was accomplished by simultaneously passing chlorides of hafnium and zirconium .(along with hydrogen, nitrogen, and methane gases) over the cemented carbide inserts. it is very difficult to characterize the exact compositions of such coatings 1 since the zirconium-to-hafnium ratio'influences the lattice-parameter as does the carbon-to-nitrogen ratio. ltwas found, however, that when the resulting lattice parameter was within the desired range described above for pure hafnium carbonitride, i.e., 4.570 to 4.630 anguncoated substrate material. Example 33. and aTiC- proved by the zirconium carbonitride coating. It is also evident that the amount of improvement obtained is strongly dependent. as in the case of hafnium carbonistrom units, excellent metal cutting performance was obtained. vSuch mixtures are accordingly included within the scope of this invention.

l. A coated cemented carbide product comprising a cemented carbide substrate and a fully dense coating selected from the group consisting of hafnium carbonitride, zirconium carbonitride and mixtures of the two, said coating firmly and adherently bonded to said substrate,

the hafnium carbonitride coating and the hafnium and zirconium carbonitride coatings having an X-ray diffraction lattice parameter within the range of about 4.570 to 4.630 angstrom units and the zirconium carbonitride coating having an X-ray diffraction parameter within the range of about 4.600 to 4.620 angstrom units.

2. The coated cemented carbide product of claim 1 in which the coating is hafnium carbonitride.

3. The coated cemented carbide product of claim 1 in which the coating is zirconium carbonitride.

4. The coated cemented carbide product of claim 1 in which the cemented carbide substrate comprises tungsten carbide and a cobalt matrix.

5. The coated cemented carbide product of claim 1 in which the cemented carbide substrate comprises tungsten carbide. titanium carbide. tantalum carbide and a cobalt matrix.

6. The coated cemented carbide product of claim 1 .crons thiek igs t i 4 ii 

1. A COATED CEMENTED CARBIDE PRODUCT COMPRISING A CEMENTED CARBIDE SUBSTRATE AND A FULLY DENSE COATING SELECTED FROM THE GROUP CONSISTING OF HAFNIUM CARBONITRIDE, ZIRCONIUM CARBONITRIDE AND MIXTURES OF THE TWO, SAID COATING FIRMYL AND ADHERENTLY BONDED TO SAID SUBSTRATE; THE HAFNIUM CARBONITRIDE COATING AND THE HAFNIUM AND ZIRCONIUM CARBONITRIDE COATINGS HAVING AN X-RAY DIFFRACTION LATTICE PARAMETER WITHIN THE RANGE OF ABOUT 4,570 TO 4.630 ANGSTROM UNITS AND THE ZIRCONIUM CARBONITRIDE COATING HAVING AN X-RAY DIFFRACTION PARAMETER WITHIN THE RANGE OF ABOUT 4.600 TO 4.620 ANGSTROM UNITS.
 2. The coated cemented carbide product of claim 1 in which the coating is hafnium carbonitride.
 3. The coated cemented carbide product of claim 1 in which the coating is zirconium carbonitride.
 4. The coated cemented carbide product of claim 1 in which the cemented carbide substrate comprises tungsten carbide and a cobalt matrix.
 5. The coated cemented carbide product of claim 1 in which the cemented carbide substrate comprises tungsten carbide, titanium carbide, tantalum carbide and a cobalt matrix.
 6. The coated cemented carbide product of claim 1 in which the carbonitride coating is from 1 to 10 microns thickness. 